Method and apparatus for sensory stimulation

ABSTRACT

An apparatus for producing an electrosensory sensation to a body member ( 120 ). The apparatus comprises one or more conducting electrodes ( 106 ), each of which is provided with an insulator ( 108 ). When the body member ( 120 ) is proximate to the conducting electrode, the insulator prevents flow of direct current from the conducting electrode to the body member. A capacitive coupling over the insulator ( 108 ) is formed between the conducting electrode ( 106 ) and the body member ( 120 ). The conducting electrodes are driven by an electrical input which comprises a low-frequency component ( 114 ) in a frequency range between 10 Hz and 500 Hz. The capacitive coupling and electrical input are dimensioned to produce an electrosensory sensation. The apparatus is capable of producing the electrosensory sensation independently of any mechanical vibration of the one or more conducting electrodes ( 106 ) or insulators ( 108 ).

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/040,389, filed Sep. 27, 2013, which is a continuation of U.S. patentapplication Ser. No. 13/432,329, filed Mar. 28, 2012, now U.S. Pat. No.8,570,163, issued Oct. 29, 2013, which is a continuation of U.S. patentapplication Ser. No. 13/171,078, filed on Jun. 28, 2011, now U.S. Pat.No. 8,174,373, issued May 8, 2012, which claims the benefit of U.S.patent application Ser. No. 12/232,548, filed on Sep. 18, 2008, now U.S.Pat. No. 7,982,588, issued Jul. 19, 2011, which claims the benefit ofpriority under 35 U.S.C. §119(e) to U.S. Provisional Application No.60/960,899, filed on Oct. 18, 2007, and which also claims priority under35 U.S.C. §119(a) to Finnish Patent Application Nos. 20075651, 20080213,20085475, and 20085472 filed in Finland on Sep. 18, 2007, Mar. 14, 2008,May 19, 2008, and May 19, 2008, respectively, the entire contents ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for sensorystimulation. The invention is particularly applicable for stimulatingthe sense of touch.

Manual input devices, such as joysticks and mice, are frequentlycomplemented by means for providing tactile sensations such that themanual input devices provide tactile feedback to their users. There arehundreds of US patents for tactile feedback devices. In most or all ofthe prior art devices the tactile stimulation is generated by means ofmoving or vibrating mechanical members. A problem shared by most suchdevices is that such moving mechanical members tend to be bulky,unreliable and/or difficult to control.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor alleviating at least one of the problems identified above.

The object of the invention is achieved by features which are disclosedin the attached independent claims. The dependent claims and the presentpatent specification disclosed additional specific embodiments andnonessential features of the invention.

The invention is based on the surprising discovery that subcutaneousPacinian corpuscles can be stimulated by means of a capacitiveelectrical coupling and an appropriately dimensioned control voltage,either without any mechanical stimulation of the Pacinian corpuscles oras an additional stimulation separate from such mechanical stimulation.An appropriately dimensioned high voltage is used as the controlvoltage. In the present context a high voltage means such a voltage thatdirect galvanic contact must be prevented for reasons of safety and/oruser comfort. This results in a capacitive coupling between the Paciniancorpuscles and the apparatus causing the stimulation, wherein one sideof the capacitive coupling is formed by at least one galvanicallyisolated electrode connected to the stimulating apparatus, while theother side, in close proximity to the electrode, is formed by the bodymember, preferably a finger, of the stimulation target, such as the userof the apparatus, and more specifically the subcutaneous Paciniancorpuscles.

Without committing themselves to any particular theory, the inventorsfind it likely that the invention is based on a controlled formation ofan electric field between an active surface of the apparatus and thebody member, such as a finger, approaching or touching it. The electricfield tends to give rise to an opposite charge on the proximate finger.A local electric field and a capacitive coupling can be formed betweenthe charges. The electric field directs a force on the charge of thefinger tissue. By appropriately altering the electric field a forcecapable of moving the tissue may arise, whereby the sensory receptorssense such movement as vibration.

A benefit of the invention is independence from mechanical vibration andits associated problems in the prior art.

An aspect of the invention is an apparatus for generating anelectrosensory stimulus to at least one body member. The apparatuscomprises one or more conducting electrodes each of which is providedwith an insulator. When the body member is proximate to the conductingelectrode, the insulator prevents flow of direct current from theconducting electrode to the body member. A capacitive coupling over theinsulator is formed between the conducting electrode and the bodymember. The apparatus also comprises a high-voltage source for applyingan electrical input to the one or more conducting electrodes, whereinthe electrical input comprises a low-frequency component in a frequencyrange between 10 Hz and 1000 Hz. The capacitive coupling and electricalinput are dimensioned to produce an electrosensory sensation which isproduced independently of any mechanical vibration of the one or moreconducting electrodes or insulators.

Another aspect of the invention is a method for causing anelectrosensory sensation to a body member. The method comprisesproviding one or more conducting electrodes. Each conducting electrodeis provided with an insulator wherein, when the body member is proximateto the conducting electrode, the insulator prevents flow of directcurrent from the conducting electrode to the body member. A capacitivecoupling over the insulator is formed between the conducting electrodeand the body member. A high-voltage source is provided for applying anelectrical input to the one or more conducting electrodes. Theelectrical input comprises a low-frequency component in a frequencyrange between 10 Hz and 1000 Hz, while the capacitive coupling andelectrical input are dimensioned to produce an electrosensory sensation.The electrosensory sensation is produced independently of any mechanicalvibration of the one or more conducting electrode(s) or insulator(s).

It is beneficial to vary the capacitive coupling such that the variationcomprises one or more frequency components in a range wherein thePacinian corpuscles exhibit their maximal sensitivity. This frequencyrange is roughly 10 to 1000 Hz and in most humans 100 to 500 Hz. Thecapacitive coupling can be varied by varying the control voltage and/orparameters of the capacitive coupling.

By way of example, the high-voltage charge applied to the electrode canhave a voltage of at least 750, 1000, 1500 or 2000 V and at most 20, 50or 100 kV (no-load measurements). In the present context, voltage valuesmay refer to voltage in direct current or effective (RMS) voltages inalternating current. The high-voltage current applied may be directcurrent or alternating current. When alternating current is being used,the frequency of the current may be high, such as at least 1 kHz, 10kHz, 20 kHz or 30 kHz and at most 100 kHz, 500 kHz tai 1 MHz, providedthat the signal also exhibits a low-frequency component, for examplesuch that high-frequency signal has an envelope whose frequencystimulates the desired sensory cells. The high-frequency alternatingcurrent can be modulated by means of a control signal having alow-frequency component, for example.

When high-voltage direct current is being used, the electrode may beembodied as a MEMS component (micro electromechanical system), whichcomprises a set of rotating, preferably individually controllable tinyelectrodes. The strength of the capacitive coupling formed by theelectrode can be adjusted by adjusting these tiny electrodes. In thiscase the strongest coupling is achieved when the tiny electrodes areoriented such that they collectively form a plane. In the inventivetechnique, by measuring the characteristics of the capacitive coupling,for example the capacitance of its variation, it may be possible tomeasure the distance of the body member from the surface of theapparatus, for example. Additionally, it may possible to detectseparately the touching of the surface by the body member. The inventivetechnique may be further enhanced by power control functionality of theelectric field being formed, for example. Utilization of someembodiments of the invention in the implementation of a proximity sensormay require a weaker electric field than what is required by causing theinventive sensory stimulus. Accordingly it may be beneficial to be ableto vary the strength of the electric field depending on the currentlyneeded functionality. Such variation may, for instance, involvestrengthening the electric field such that a sense of touch or vibrationis caused in the body member when it is brought sufficiently close tothe electrode or insulator.

By way of example, the low-frequency component of the control signalbeing used in the inventive technique may be generated by modulating ahigh-frequency alternating current. The modulation signal may becontinuous or pulsed, for example. The duration of individual pulses maybe 0.01, 0.5 or 4 ms and the pause between pulses can be at least 1, 10or 100 ms.

The low-frequency component of the control signal may have a frequencyof at least 10, 50 or 100 Hz and at most 300, 500 or 1000 Hz. In onespecific embodiment the control signal has an exemplary frequency of 120Hz. In the inventive technique the alternating electric field, whichcauses the stimulus to be provided, may exhibit an intensity peak of atleast 100 V/mm, 200 V/mm or 500 V/mm and at most 10 kV/mm, 30 kV/mm or100 kV/mm. The field strength may be measured, for example, by means ofa grounded electrode with a surface area of eg 1 cm² positioned 0.05 to5 mm, preferably about 1 mm from the surface of the insulated electrode.

By way of example, the electric field generated by the electrode can becontrolled according to a processing logic being executed in a computeror other electronic data processing apparatus. For example, the controllogic can be used to control the variation frequency and/or intensity ofthe electric field generated by an individual electrode. Furthermore,the control logic can be used to pulse the varying electric field, forexample. The control logic can also receive control information via adata network from a another apparatus, such as another computer or dataprocessing apparatus.

An inventive apparatus for sensory stimulation comprises at least oneinsulated electrode, wherein the apparatus is operable to apply a chargeto the electrode such that the charge causes a stimulation of thePacinian corpuscles. For humans this normally requires a voltage of atleast 750 V. The apparatus further comprises means for varying theintensity of the charge-generated, capacitively-coupled electric fieldby utilizing a signal having a component with a frequency of at least 10Hz and at most 1000 Hz.

Some embodiments of the inventive apparatus can be implemented, when sodesired, without mechanically moving parts, and such embodiments do notpose similar restrictions on the mechanical characteristics of thematerials as do actuators based on mechanical movement of the surface.Accordingly, some embodiments of the invention are applicable to a widevariety of surfaces of different shapes. For instance, the surface shapeof the electrode and/or insulator attached to it may be planar, rounded,spherical or concave. Likewise, the insulator material can be selectedfrom a variety of materials having characteristics particularly suitablefor the chosen application. As regards mechanical characteristics, thesurface material can be hard, soft, stiff, bending, transparent orflexible. The surface, as well as the material being used as theconductor, can also be transparent.

An individual electrode of the apparatus and/or the insulator attachedto the electrode can have a surface area of 0.1, 1, 10 or 100 cm² ormore. The apparatus can comprise multiple insulated electrodes which canbe arranged in an array forming an X-Y coordinate system. Each electrodeof such a system can, when so desired, be controlled by a control logicaccording to some embodiments of the invention, for example. Theelectrodes can be fixedly mounted or movable.

The apparatus may comprise means for varying the variation frequency ofthe electric field, for example by modulating the high-voltagealternating current or by moving the electrodes of the MEMS deviceaccording to the control signal.

The insulator to be arranged between the electrode of the apparatus andthe body member can have a thickness of at least 0.01 mm, 0.05 mm, 0.1mm or 0.5 mm and at most 10 mm, 20 mm or 50 mm. The insulator materialcan be selected according to the intended use and/or voltage to be used,for example.

In some embodiments the insulator comprises multiple layers. Forinstance, the inventors have discovered that the bulk of the insulatorlayer between the electrode and the body part approaching or toughing itmay comprise glass but glass is not optimal as the insulator's surfacematerial. In the present context, optimal means an insulator materialwhich best supports the creation of the electrosensory sensation. Aglass insulator works much better if covered with a plastic film.

The inventive apparatus can be implemented such that its powerconsumption is low. For example, the power required to cause a sensorystimulus may be 1 mW, 5 mW or 10 mW or more. Power consumption can bemeasured on the basis of the electric power applied to the electrodewhen a human touches the apparatus surface or when a capacitivelygrounded 50 pF capacitor is connected to the apparatus surface.

The apparatus may comprise means for measuring the capacitance of thecapacitive coupling being formed. The apparatus may further comprisemeans for adjusting the characteristics of the electric field, such asintensity or variation frequency, based on the obtained measurementinformation.

The inventive apparatus for sensory stimulation can be integrated as apart of some other apparatus or system. For instance, a prior art touchdisplay can be complemented by apparatuses according to some embodimentsof the present invention. This way it is possible to provide a touchdisplay which produces a sensation of touch even if the display is notphysically touched. Control components of the feedback system can becombined, or they may be arranged to exchange information with oneanother. An advantageous embodiment of the presently disclosed methodand apparatus is a control device based on touch or proximity, such as atouch display that produces a feedback which can be sensed via the senseof touch.

In some embodiments of the invention, the local charge/field can becontrolled by means of capacitive grounding. In various embodiments ofthe invention, it is possible to into account the fact that thedependence of the electric coupling on the insulated electrode, ie,capacitance, depends on several factors. The capacitance value affectsthe potential difference between the finger and electrode if theapparatus or subject (such as human) is not grounded, and their groundpotential is determined via stray capacitances. Prior artimplementations ignore control and processing of the distribution ofcapacitances and voltages, and some embodiments of the present inventionaim at alleviating this separate problem.

For example, the invention differs from prior art solutions in that notouching or mechanical movement or vibration is required to generate thestimulus. Accordingly, the invention provides advantages over solutionswhich are based on, say, stroking the finger over the electrodes and onlocally varying friction caused by the electric field. Furthermore, thevarious embodiments of the invention support solutions which are basednot only on alternating current but also on direct current. Yet further,the inventive solution can be provided with a functionality to detectproximity and touch, whereby the same component can be used for inputand output functions. In addition, various embodiments of the inventionmay utilize thick insulators, for example, which are mechanicallystronger than thin insulators. Moreover, it has been discovered inconnection with several embodiments of the invention that it isbeneficial to use particular variation frequencies for the electricfield, as they will enable smaller energy consumption in the generationof the stimulus.

In one embodiment the electrical input also comprises a high-frequencycomponent having a frequency which is higher than the frequency of thelow-frequency component and lower than 500 kHz. This embodiment may alsocomprise a modulator or other means for modulating the high-frequencycomponent by the low-frequency component.

The electrical input to the one or more conducting electrodes has apeak-to-peak voltage of 750 to 100,000 Volts and the insulator should bedimensioned accordingly. In practical implementations with currentlyavailable materials the insulator thickness is typically between 0.1 mmand 50 mm.

In order to convey time-variant information, as opposed to asteady-state sensation, the apparatus may comprise means for modulatingthe electrical input according to the time-variant information.

A simple but effective implementation of the invention comprisesprecisely one conducting electrode for each spatially distinct area ofthe body member. There may be more than one conducting electrode suchthat each conducting electrode stimulates a spatially distinct area ofone or more body members. The apparatus may comprise an enclosure whichcontains the high voltage source which is common to all the severalconducting electrodes and wherein the enclosure also contains means forconveying the electrical input to zero or more of the several conductingelectrodes simultaneously. The inventive apparatus and/or the one ormore conducting electrodes may be positioned such that that the bodymember most likely to be affected is part of a human hand. For example,five conducting electrodes under control of a common controller, maystimulate, at different times, zero to five fingertips in parallel. Thefive conducting electrodes thus convey five bits of information inparallel. The apparatus may be implemented as part of an input/outputperipheral device connectable to a data processing equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of specific embodiments with reference to the attached drawings,in which

FIG. 1 illustrates the operating principle of a capacitiveelectrosensory interface (“CEI”);

FIG. 2 illustrates an embodiment of the CEI;

FIG. 3 shows an enhanced embodiment with multipleindependently-controllable electrodes;

FIG. 4 shows a specific implementation of the embodiment shown in FIG.3;

FIG. 5 is a graph which schematically illustrates the sensitivity of atest subject to sensations produced by the inventive capacitiveelectrosensory interface at various frequencies;

FIG. 6 is a graph which further clarifies the operating principle of theCEI;

FIGS. 7A and 7B show an implementation of the CEI wherein the strengthof the capacitive coupling is adjusted by electrode movement;

FIG. 8 shows an implementation of the CEI wherein the charges ofdifferent electrodes have opposite signs;

FIG. 9 shows an implementation of the CEI wherein a group of electrodesare organized in the form of a matrix;

FIG. 10 illustrates distribution of an electric field-generatingpotential in capacitive couplings when the apparatus is grounded;

FIG. 11 illustrates distribution of an electric field-generatingpotential in capacitive couplings when the apparatus is floating (notgrounded);

FIG. 12 illustrates distribution of an electric field-generatingpotential in capacitive couplings when the apparatus is floating and theuser is sufficiently close to the apparatus and capacitively grounded tothe ground (reference) potential of the apparatus;

FIG. 13 shows an arrangement wherein capacitive couplings are utilizedto detect touching; and

FIGS. 14 and 15 illustrate embodiments in which a single electrode andtemporal variations in the intensity of the electrosensory stimulus canbe used to create illusions of a textured touch screen surface.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1 through 15 relate to the operation and implementation of acapacitive electrosensory interface (“CEI”) which can be employed in theinventive touch screen interface.

FIG. 1 illustrates the operating principle of the CEI. Reference numeral100 denotes a high-voltage amplifier. The output of the high-voltageamplifier 100, denoted OUT, is coupled to an electrode 106 which isinsulated against galvanic contact by an insulator 108 which comprisesat least one insulation layer or member. Reference numeral 120 generallydenotes a body member to be stimulated, such as a human finger. Humanskin, which is denoted by reference numeral 121, is a relatively goodinsulator when dry, but the CEI provides a relatively good capacitivecoupling between the electrode 106 and the body member 120. Thecapacitive coupling is virtually independent from skin conditions, suchas moisture. The inventors' hypothesis is that the capacitive couplingbetween the electrode 106 and the body member 120 generates a pulsatingCoulomb force. The pulsating Coulomb force stimulatesvibration-sensitive receptors, mainly those called Pacinian corpuscleswhich reside under the outermost layer of skin in the ipodermis 121. ThePacinian corpuscles are denoted by reference numeral 122. They are shownschematically and greatly magnified.

The high-voltage amplifier 100 is driven by an input signal IN whichresults in a substantial portion of the energy content of the resultingCoulomb forces to reside in a frequency range to which the Paciniancorpuscles 122 are sensitive. For humans this frequency range is between10 Hz and 1000 Hz, preferably between 50 Hz and 500 Hz and optimallybetween 100 Hz and 300 Hz, such as about 240 Hz. The frequency responseof the Pacinian corpuscles is further discussed in connection with FIGS.5 and 6.

It should be understood that, while “tactile” is frequently defined asrelating to a sensation of touch or pressure, the electrosensoryinterface according to the present CEI, when properly dimensioned, iscapable of creating a sensation of vibration to a body member even whenthe body member 120 does not actually touch the insulator 108 overlayingthe electrode 106. This means that unless the electrode 106 and/orinsulator 108 are very rigid, the pulsating Coulomb forces between theelectrode 106 and body member 120 (particularly the Pacinian corpuscles122) may cause some slight mechanical vibration of the electrode 106and/or insulator 108, but the method and apparatus according to the CEIare capable of producing the electrosensory sensation independently ofsuch mechanical vibration.

The high-voltage amplifier and the capacitive coupling over theinsulator 108 are dimensioned such that the Pacinian corpuscles or othermechanoreceptors are stimulated and an electrosensory sensation (asensation of apparent vibration) is produced. For this, the high-voltageamplifier 100 must be capable of generating an output of several hundredvolts or even several kilo volts. In practice, the alternating currentdriven into the body member 120 has a very small magnitude and can befurther reduced by using a low-frequency alternating current.

FIG. 2 illustrates an apparatus which implements an illustrativeembodiment of the present CEI. In this embodiment the high-voltageamplifier 100 is implemented as a current amplifier 102 followed by ahigh-voltage transformer 104. In the embodiment shown in FIG. 2, thesecondary winding of the high-voltage transformer 104 is in a more orless flying configuration with respect to the remainder of theapparatus. The amplifier 100, 102 is driven with a modulated signalwhose components are denoted by 112 and 114. The output of thehigh-voltage amplifier 100 is coupled to an electrode 106 which isinsulated against galvanic contact by the insulator 108. Referencenumeral 120 generally denotes a member to be stimulated, such as a humanfinger. Human skin, which is denoted by reference numeral 121, is arelatively good insulator when dry, but the CEI provides a relativelygood capacitive coupling between the electrode 106 and the electricallyconductive tissue underneath the skin surface 121. Mechanoreceptors,such as the Pacinian corpuscles 122, reside in this conductive tissue.In FIGS. 1 and 2, the Pacinian corpuscles 122 are shown schematicallyand greatly magnified.

A benefit of the capacitive coupling between the electrode 106 and theelectrically conductive tissue underneath the skin surface, which isknown as the Corneus Layer and which contains the Pacinian corpuscles122, is that the capacitive coupling eliminates high local currentdensities to finger tissue, which would result from contact that isconductive at direct current.

It is beneficial, although not strictly necessary, to provide agrounding connection which helps to bring the subject to be stimulated,such as the user of the apparatus, closer to a well-defined(non-floating) potential with respect to the high-voltage section of theapparatus. In the embodiment shown in FIG. 2, the grounding connection,denoted by reference numeral 210, connects a reference point REF of thehigh-voltage section to a body part 222 which is different from the bodypart(s) 120 to be stimulated. In the embodiment shown in FIG. 2, thereference point REF is at one end of the secondary winding of thetransformer 104, while the drive voltage for the electrode(s) 206A,206B, 206C is obtained from the opposite end of the secondary winding.

In an illustrative implementation, the apparatus is a hand-held devicewhich comprises a touch display activated by finger(s) 120. Thegrounding connection 210 terminates at a grounding electrode 212. Anillustrative implementation of the grounding electrode 212 is one ormore ground plates which are arranged such that they are convenientlytouched one hand 222 of the user while the apparatus is manipulated bythe other hand. The ground plate(s) may be positioned on the same sideof the apparatus with the touch display and next to the touch display,or it/they may be positioned on adjacent or opposite side(s) from theside which comprises the touch display, depending on ergonomicconsiderations, for example.

In real-world apparatuses, the coupling 210 between the reference pointREF and the non-stimulated body part 222 may be electrically complex. Inaddition, hand-held apparatuses typically lack a solid referencepotential with respect to the surroundings. Accordingly, the term“grounding connection” does not require a connection to a solid-earthground. Instead the grounding connection means any connection whichhelps to decrease the potential difference between the referencepotential of the apparatus and a second body member distinct from thebody member(s) to be stimulated. This definition does not rule out anycapacitive parallel or stray elements, so long as the groundingconnection 210 helps bring the user of the apparatus, along with thenon-stimulated body part 222, to a potential which is reasonably welldefined with respect to the high-voltage section of the apparatus. Acapacitive grounding connection will be discussed in connection withFIG. 12. In the present context, the reasonably well-defined potentialshould be understood in view of the voltage OUT which drives theelectrode(s) 206A, 206B, 206C. If the electrode drive voltage OUT is,say, 1000 V, a potential difference of, say, 100 V, between the user'sbody and the reference point REF may not be significant.

The non-capacitive coupling 210 between the reference point REF of thehigh-voltage section and the non-stimulated body part 222 greatlyenhances the electrosensory stimulus experienced by the stimulated bodypart 120. Conversely, an equivalent electrosensory stimulus can beachieved with a much lower voltage and/or over a thicker insulator whenthe non-capacitive coupling 210 is being used.

The amplifier 100, 102 is driven with a high-frequency signal 112 whichis modulated by a low-frequency signal 114 in a modulator 110. Thefrequency of the low-frequency signal 114 is such that the Paciniancorpuscles, which reside in the electrically conductive tissueunderneath the skin surface, are responsive to that frequency. Thefrequency of the high-frequency signal 112 is preferably slightly abovethe hearing ability of humans, such as 18 to 25 kHz, more preferablybetween about 19 and 22 kHz. If the frequency of the signal 112 iswithin the audible range of humans, the apparatus and/or its drivecircuit may produce distracting sounds. On the other hand, if thefrequency of the signal 112 is far above the audible range of humans,the apparatus drives more current into the member 120. A frequency ofabout 20 kHz is advantageous in the sense that components designed foraudio circuits can generally be used, while the 20 kHz frequency isinaudible to most humans. Experiments carried out by the inventorssuggest that such modulation is not essential for the CEI. Use of ahigh-frequency signal with low-frequency modulation, such as the oneschematically shown in FIG. 2, as opposed to a system which relies onthe low-frequency signal alone, provides the benefit that the relativelyhigh alternating voltage (a few hundred volts or a few kilovolts) can begenerated with a relatively small transformer 104.

Terms like frequency or kHz should not be understood such that the high-or low-frequency signals 112, 114 are restricted to sinusoidal signals,and many other waveforms can be used, including square waves. Theelectrical components, such as the modulator 110, amplifier 102 and/ortransformer 104 can be dimensioned such that harmonic overtones aresuppressed. The inventors have discovered that pulses with durations of4 ms (approximately one half-cycle of the low-frequency signal) orlonger can be readily detected and with a practical insulator thicknessthe peak-to-peak voltage in the electrode 106 needs to be at least about750 V. Unloaded peak-to-peak voltage measured in the electrode 106should be in the range of approximately 750 V-100 kV. Near the lowerlimit of this voltage range, the insulator thickness may be 0.05-1 mm,for example. As material technology and nanotechnology develop, eventhinner durable insulating surfaces may become available. This may alsopermit a reduction of the voltages used.

The elements of FIGS. 1 and 2 described so far produce a steady-stateelectrosensory sensation as long as the body member, such as the finger120, is in the vicinity of the electrode 106. In order to convey usefulinformation, the electrosensory sensation must be modulated. In somesimple embodiments, such modulation can be implemented by positioningthe electrode 106 such that useful information is conveyed by the factthat the finger 120 can sense the presence of the electrode 106. Forexample, the electrode 106 can be positioned over a switch, or in thevicinity of it, such that the switch can be detected without having tosee it.

In other embodiments, such information-carrying modulation can beprovided by electronically controlling one or more operating parametersof the inventive apparatus. The information-carrying modulation shouldnot be confused with the modulation of the high-frequency signal 112 bythe low-frequency signal 114, the purpose of which is to reduce the sizeof the transformer 104. In the schematic drawing shown in FIG. 2, suchinformation-carrying modulation is provided by controller 116, whichcontrols one or more of the operating parameters of the inventiveapparatus. For instance, the controller 116 may enable, disable or alterthe frequency or amplitude of the high- or low-frequency signals 112,114, the gain of the amplifier 102, or it may controllably enable ordisable the power supply (not shown separately) or controllably breakthe circuit at any point.

FIG. 3 shows an enhanced embodiment of the inventive apparatus withmultiple independently-controllable electrodes. In FIG. 3, elements withreference numerals less than 200 have been described in connection withFIGS. 1 and 2, and a repeated description is omitted. This embodimentcomprises multiple independently-controllable electrodes 206A, 206B and206C, of which three are shown but this number is purely arbitrary.Reference numeral 216 denotes an implementation of a controller whichcontrols a switch matrix 217 which provides the high-voltage signal OUTto the electrodes 206A, 206B and 206C under control of the controller216. The controller 216 may be responsive to commands from an externaldevice, such as a data processing equipment (not shown separately).

A benefit of the embodiment shown in FIG. 3 is that virtually all thedrive circuitry, including the high-voltage amplifier 100, controller216, and switch matrix 217, can be integrated into a common enclosurewhich is denoted by reference numeral 200. In this embodiment only theelectrodes 206A, 206B and 206C and a single connecting wire for eachelectrode are outside the enclosure 200. As stated earlier, theelectrodes need to be nothing more than simple conducting orsemi-conducting plates covered by appropriate insulators. Therefore theenclosure 200 can be positioned in virtually any convenient positionbecause the only elements external to it are very simple electrodes andconnecting wires (and, in some implementations a power supply, not shownseparately).

Some prior art systems provide direct stimulation of nerves via galvaniccurrent conduction to the outermost layer of the skin. Because of thegalvanic current conduction, such systems require two electrodes tostimulate an area of skin. In contrast to such prior art systems, theembodiment described in connection with FIG. 3 involves multipleelectrodes 206A, 206B and 206C, but each electrode alone stimulates adistinct area of skin, or more precisely, the mechanoreceptors,including the Pacinian corpuscles underlying the outermost layers ofskin. Therefore a configuration of n electrodes conveys n bits ofinformation in parallel.

FIG. 4 shows a specific implementation of the embodiment shown in FIG.3. In this implementation the switch matrix 217 comprises a bank oftriacs 207A, 207B and 207C, but other types of semiconductor switchescan be used, including semiconductor relays. Conventionalelectromechanical relays can be used as well. In this embodiment theswitches (triacs) 207A, 207B and 207C are positioned logically after thetransformer 104, ie, in the high-voltage circuitry. This implementationrequires high-voltage switches (several hundred volts or severalkilovolts) but it provides the benefit that the remainder of thecircuitry, including the elements 100 through 114, can serve all of theelectrodes 206A, 206B and 206C. As shown in FIG. 4, the controller 216may be connectable to a data processing equipment, an example of whichis shown here as a personal computer PC.

FIG. 5 is a graph which schematically illustrates the sensitivity of arandomly selected test subject to sensations produced by an apparatussubstantially similar to the one shown in FIG. 2. The x-axis of thegraph shows frequency of the low-frequency signal (item 114 in FIG. 2)multiplied by two, while the y-axis shows the amplitude required todetect an electrosensory stimulation. The amplitude scale is relative.The small dip at 75 Hz may be a measurement anomaly. The reason forplacing the doubled low-frequency signal on the x-axis is that theCoulomb forces between the electrode 106 and the body member 120 havetwo intensity peaks for each cycle of a sinusoidal low-frequency signal,as will be schematically illustrated in connection with FIG. 6.

The relative sensitivity at various frequencies is remarkably similar tothe one published in section 2.3.1 (FIG. 2.2) of Reference document 1.Reference document 1 relates to vibrotactile (mechanical) stimulation ofskin, but the similarity of the frequency response shown in FIG. 5 tothe one published in Reference 1 suggests that the present CEI operatessuch that the electrode 106 and the sensitive member 120 (see FIG. 1)form a capacitor over the insulator 108, and in that capacitor theoscillating Coulomb forces are converted to mechanical vibrations whichare sensed by mechanoreceptors, including the Pacinian corpuscles. Theinventors have also studied an alternative hypothesis wherein thePacinian corpuscles are stimulated by current flowing through them, butthis hypothesis does not explain the observations as well as the onewhich is based on Coulomb forces acting on the Pacinian corpuscles.However, the technical CEI described herein does not depend on thecorrectness of any particular hypothesis attempting to explain why theCEI operates the way it does.

FIG. 6 is a graph which further clarifies the operating principle of theCEI and the interpretation of frequencies in connection with the presentCEI. Reference numeral 61 denotes the low-frequency input signal to themodulator 110 (shown as item 114 in FIG. 2). Reference numeral 62denotes the output of the modulator, ie, the high-frequency input signalas modulated by the low-frequency input signal.

Reference numerals 63 and 64 denote the resulting Coulomb forces in thecapacitive coupling between the electrode 106 and the body member 120over the insulator 108. Because the two sides of the capacitive couplinghave opposite charges, the Coulomb force between the two sides is alwaysattractive and proportional to the square of the voltage. Referencenumeral 63 denotes the actual Coulomb force while reference numeral 64denotes its envelope. The envelope 64 is within the range of frequenciesto which the Pacinian corpuscles are sensitive, but because the Coulombforce is always attractive, the envelope 64 has two peaks for each cycleof the modulator output signal 62, whereby a frequency-doubling effectis produced. Because the Coulomb force is proportional to the square ofthe voltage, any exemplary voltages disclosed herein should beinterpreted as effective (RMS) values in case the voltages are notsinusoidal.

The statement that the two sides of the capacitive coupling haveopposite charges whereby the Coulomb force is always attractive holdsfor a case in which the apparatus and the body member to be stimulatedare at or near the same potential. High static charges can causedeviations from this ideal state of affairs, which is why some form ofgrounding connection between a reference potential of the high-voltagesource and the body element other than the one(s) to be stimulated isrecommended, as the grounding connection helps to lower the potentialdifferences between the apparatus and its user.

The CEI can be implemented as part of an input/output peripheral devicewhich is connectable to a data processing equipment. In such aconfiguration the data processing equipment can provide prompting and/orfeedback via electrically-controllable electrosensory sensation.

FIGS. 7A and 7B show implementations of the CEI wherein the strength ofthe capacitive coupling is adjusted by electrode movement. Generation ofthe electric field, and its variation as necessary, is effected via aset of electrodes 704 which comprises individual electrodes 703. Theindividual electrodes 703 are preferably individually controllable,wherein the controlling of an electrode affects its orientation and/orprotrusion. FIG. 7A shows an implementation wherein a group ofelectrodes 703 are oriented, via the output signal from the controller216, such that the electrodes 703 collectively form a plane under theinsulator 702. In this situation the high-voltage current (DC or AC)from the high-voltage amplifier 100 to the electrodes 703 generates anopposite-signed charge of sufficient strength to a body member (eg thefinger 120) in close proximity to the apparatus. A capacitive couplingbetween the body member and the apparatus is formed over the insulator702, which may give rise to a sensory stimulus.

FIG. 7B shows the same apparatus shown in FIG. 7A, but in this case thestrength of the capacitive coupling generated with the current from thehigh-voltage amplifier 100 is minimized by orienting the electrodes (nowshown by reference numeral 714) such that they do not form a plane underthe insulator 702. In some implementations of the present invention, theelectric field alternating with a low frequency can be generated byalternating the state of the apparatus between the two states shown inFIGS. 7A and 7B. The frequency of the state alternation can be in theorder of several hundred, eg 200 to 300 full cycles per second.

FIG. 8 shows an implementation of the CEI wherein the individualelectrodes 803 in the set of electrodes 804 may have charges of oppositesigns. The charges of individual electrodes 803 may be adjusted andcontrolled via the controller 216. The individual electrodes 803 may beseparated by insulator elements 806, so as the prevent sparking orshorting between the electrodes. The capacitive coupling between the CEIand the body member proximate to it may give rise to areas havingcharges with opposite signs 801. Such opposing charges are mutuallyattractive to one another. Hence it is possible that Coulomb forcesstimulating the Pacinian corpuscles may be generated not only betweenthe CEI and the body member but between infinitesimal areas within thebody member itself.

FIG. 9 shows an implementation of the CEI wherein a group ofindividually controllable electrodes 910 a through 910 i are organizedin the form of a matrix. Such a matrix can be integrated into a touchscreen device, for example. Since the CEI described above does notrequire direct connection (touching) between the CEI and a body memberof its user, the electrodes of the CEI apparatus can be positionedbehind the touch screen, wherein “behind” means the side of the touchscreen opposite to the side facing the user during normal operation.Alternatively, the electrodes can be very thin and/or transparent,whereby the electrodes can overlay the touch screen on the side normallyfacing the user. The electric charges, which are conducted from thehigh-voltage amplifier 100 to the electrodes 910 a through 910 i via theswitch array 217, may all have similar signs or the charges conducted todifferent electrodes may have different signs, as illustrated inconnection with FIG. 8. For instance, the controller 216 may control theswitches in the switch array individually, or certain groups may formcommonly-controllable groups. The surface of an individual electrodeand/or its associated insulator can be specified according to theintended range of operations or applications. The minimum practical areais about 0.01 cm², while the practical maximum is roughly equal to thesize of a human hand. It is expected that surface areas between 0.1 and1 cm² will be found most usable in practice.

The matrix of electrodes 910 a through 910 i and the switch array 217provide a spatial variation of the electrosensory stimulation. In otherwords, the sensory stimulation provided to the user depends on thelocation of the user's body member, such as a finger, proximate to theCEI apparatus which is integrated to the inventive touch screen. Thespatially varying sensory stimulation provides the user with anindication of the layout of the touch-sensitive areas of the touchscreen interface.

In addition to the spatially varying sensory stimulation, the controller216 may direct the switch array 217 to produce a temporally varying(time-dependent) electrosensory stimulation, which can be used for awide variety of useful effects. For instance, the temporally varyingelectrosensory stimulation can be used to indicate a detected activationof a touch-sensitive area (“key press”). This embodiment address acommon problem associated with prior art touch screen devices, namelythe fact that a detection of a key press produces no tactile feedback.Prior art application-level programs used via touch screen devices mayprovide visual or aural feedback, but such types of feedback exhibit thevarious problems described earlier. In addition, production of thevisual or aural feedback from the application-level program causes aburden on the programming and execution of those programs. In someimplementations of the invention, an interface-level or driver-levelprogram provides a tactile feedback from a detected activation of atouch-sensitive area by using the temporally and spatially variantelectrosensory stimulation, and such interface-level or driver-levelprograms can be used by any application-level programs. For example, theapplication-level programs can be coupled to the inventive touch screeninterface via an application programming interface (“API”) whose set ofavailable functions includes the feedback generation described above.

The temporally and spatially variant electrosensory stimulation can alsobe used to change the layout of the touch-sensitive areas “on the fly”.In hindsight, this operation may be considered roughly analogous tochanging the keyboard or keypad layout depending on the applicationprogram or user interface screen currently executed. However, when priorart touch screen devices change keyboard or keypad layout on the fly,the new layout must be somehow indicated to the user, and this normallyrequires that the user sees the touch screen device.

Some embodiments of the inventive touch screen device eliminate the needto see the touch screen device, assuming that the layout of thetouch-sensitive areas is sufficiently simple. For instance, up to abouttwo dozen different “key legends” can be indicated to the user byproviding different patterns for the temporally and spatially variantelectrosensory stimulation. As used herein, the expression “key legend”refers to the fact that prior art touch screen devices, which produce notactile feedback, normally produce visual cues, and these are commonlycalled “legends”. In some embodiments of the present invention, thefunction of the key legends can be provided via different patterns. Forinstance, the following patterns can be identified with one fingertip:pulses with low, medium or high repetition rate; sweeps to left, right,up or down, each with a few different repetition rates; rotationsclockwise or anti-clockwise, each with a few different repetition rates.

From the above, it is evident that the inventive electrosensoryinterface can produce a large number of different touch-sensitive areas,each with a distinct “feel” (technically: a different pattern for thetemporal and spatial variation of the electrosensory stimulus). Hencethe screen section of a conventional touch screen is not absolutelyneeded in connection with the present invention, and the term touchdevice interface should be interpreted as an interface device which,among other things, is suitable for applications commonly associatedwith touch screen devices, although the presence of the screen is notmandatory.

Moreover, the strength of the capacitive coupling between the inventiveCEI and a body member of its user (or the capacitive coupling between anindividual electrode or a group of electrodes and the user's bodymember) can be determined by direct or indirect measurements. Thismeasurement information can be utilized in various ways. For instance,the strength of the capacitive coupling can indicate the body member'sproximity to the electrode, or it can indicate touching the electrode bythe body member. Such measurement functionality can be provided by adedicated measurement unit (not shown) or it can be integrated into oneof the blocks described earlier, such as the switch matrix 217. Theswitch matrix 217 (or the optional dedicated measurement unit) can sendthe measurement information to the controller 216 which can utilize itto vary the electric fields generated by the electrodes, by varying thevoltage or frequency. In addition or alternatively the controller 216may forward the measurement information, or some information processedfrom it, to a data processing equipment, such as the personal computerPC shown in FIG. 4.

Yet further two or more inventive touch device interfaces can beinterconnected via some communication network(s) and data processingequipment. In such an arrangement, the electrosensory stimulationprovided to the users of the touch screen devices may be based on somefunction of all users' contribution to the proximity to their respectivedevices. In one illustrative example, such an interconnection of two (ormore) touch screen devices can provide their users with tactile feedbackwhose strength depends on the sum of the areas of hands touch thetouch-sensitive areas. This technique simulates a handshake whosestrength reflects the sum of hand pressure exerted by both (or all)users. In another illustrative example, a music teacher might “sense”how a remotely located student presses the keys of a simulated pianokeyboard.

FIGS. 10 through 13 are equivalent circuits (theoretical models) whichmay be useful in dimensioning the parameters of the capacitive coupling.FIG. 10 illustrates distribution of an electric field-generatingpotential in capacitive couplings when the apparatus is grounded. Theunderlying theory is omitted here, and it suffices to say that in thearrangement shown in FIG. 10, the drive voltage e of an electrode isdivided based on the ratio of capacitances C1 and C2, wherein C1 is thecapacitance between the finger and the electrode and C2 is the straycapacitance of the user. The electric field experienced by the finger iscaused by voltage U1:

$U_{1} = {\frac{C_{2}}{C_{1} + C_{2}}e}$

This voltage is lower than the drive voltage e from the voltage source.In a general case the reference potential of the apparatus may befloating, as will be shown in FIG. 11. This arrangement furtherdecreases the electric field directed to the body member, such asfinger.

For these reasons some embodiments of the invention aim at keeping thecapacitance C1 low in comparison to that of C2. At least capacitance C1should not be significantly higher than C2. Some embodiments aim atadjusting or controlling C2, for instance by coupling the referencepotential of the apparatus back to the user, as shown in FIG. 12.

Further analysis of the actual value of capacitance C1 shows that it canbe treated as a capacitance consisting of three series-coupled partialcapacitances: C₁ of the insulator material, C_(a) of the air gap betweeninsulator and finger, and C_(s) formed by the outmost skin layer that iselectrically insulating the inner, conducting tissue from theenvironment. Each partial capacitance is given by:

$C = {ɛ\frac{S}{d}}$

Herein, ∈ is the permittivity (dielectric constant) of the insulatingmaterial, S is the (effective) surface area and d is the distancebetween the surfaces of the capacitor. In a series arrangement ofcapacitances, the smallest one of the individual capacitances dominatesthe overall value of the total capacitance C1. When the body member doesnot touch the surface of the insulated electrode but only approaches it,the capacitive coupling is weak. Thus the value of C1 is small andmainly determined by the air gap, C_(a). When the body member touchesthe surface, the effective air gap is small (approximately the heightridges of the fingerprint profile on the skin surface). As capacitanceis inversely proportional to the distance of the conducting surfacesforming the capacitor, corresponding C_(a) obtains a high value, and thevalue of C1 is determined by C_(i) and C_(s). Thus the effectiveness ofthe electrosensory stimulus generation can be enhanced by appropriateselection of insulator material, particularly in terms of thickness anddielectric properties. For instance, selecting a material with arelatively high dielectric constant for the insulator reduces theelectric field in the material but increases the electric field strengthin the air gap and skin.

Furthermore, in applications where the surface is likely to be touchedwhile the electrosensory stimulation or response is given, theeffectiveness of the electrosensory stimulus generation can be enhancedby optimal selection of the material that will be touched by the bodymember. This is particularly significant in connection with insulatorswhich are good volume insulators (insulators in the direction of thesurface's normal) but less so in the direction along the surface.

An insulator's insulation capability along the surface may be negativelyaffected by surface impurities or moisture which have a negative effecton the apparent strength of the sensation felt by the body member to bestimulated. For instance, glass is generally considered a goodinsulator, but its surface tends to collect a thin sheet of moisturefrom the air. If the electrode of the CEI is insulated with glass, theelectrosensory effect is felt in close proximity (when there is still anair gap between body member and the glass surface). However, when theglass surface is touched, even lightly, the electrosensory tends toweaken or disappear altogether. Coating the outer insulating surfacewith a material having a low surface conductance remedies such problems.The inventors speculate that if the surface having some surfaceconductivity is touched, it is the conductive layer on the surface thatexperiences the coulomb force rather than the body member touching thesurface. Instead the touching body member acts as a kind of groundingfor the conductive surface layer, for example via the stray capacitanceof the body.

Instead of the measures described in connection with FIGS. 10 through12, or in addition to such measures, stray capacitances can becontrolled by arrangements in which several electrodes are used togenerate potential differences among different areas of the touch screensurface. By way of example, this technique can be implemented byarranging the touch-sensitive surface of a hand-held device (eg the topside of the device) to a first potential, while the opposite side isarranged to a second potential, wherein the two different potentials canbe the positive and negative poles of the device. Alternatively, a firstsurface area can be the electric ground (reference potential), while asecond surface area is charged to a high potential.

Moreover, within the constraints imposed by the insulator layer(s), itis possible to form minuscule areas of different potentials, such aspotentials with opposite signs or widely different magnitudes, whereinthe areas are small enough that the user's body member, such as finger,is simultaneously subjected to the electric fields from several areaswith different potentials.

FIG. 13 shows an embodiment in which the capacitive coupling is utilizedto detect touching or approaching by the user's body member, such asfinger. A detected touching or approaching by the user's body member canbe passed as an input to a data processing device. In the embodimentshown in FIG. 13, the voltage source is floating. A floating voltagesource can be implemented, via inductive or capacitive coupling and/orwith break-before-make switches. A secondary winding of a transformer isan example of a simple yet effective floating voltage source. Bymeasuring the voltage U4, it is possible to detect a change in thevalue(s) of capacitance(s) C1 and/or C2. Assuming that the floatingvoltage source is a secondary winding of a transformer, the change incapacitance(s) can be detected on the primary side as well, for exampleas a change in load impedance. Such a change in capacitance(s) serves asan indication of a touching or approaching body member.

In one implementation, the apparatus is arranged to utilize suchindication of the touching or approaching body member such that theapparatus uses a first (lower) voltage to detect the touching orapproaching by the body member and a second (higher) voltage to providefeedback to the user. For instance, such feedback can indicate any ofthe following: the outline of the/each touch-sensitive area, a detectionof the touching or approaching body member by the apparatus, thesignificance of (the act to be initiated by) the touch-sensitive area,or any other information processed by the application program and whichis potentially useful to the user.

FIG. 14 schematically illustrates an embodiment in which a singleelectrode and temporal variations in the intensity of the electrosensorystimulus can be used to create illusions of a textured touch screensurface. Reference numeral 1400 denotes a touch-sensitive screen which,for the purposes of describing the present embodiment, comprises threetouch-sensitive areas A₁, A₂ and A₃. The approaching or touching by thetouch-sensitive areas A₁, A₂ and A₃ of a user's finger 120 is detectedby a controller 1406.

According to an embodiment of the invention, a conventionaltouch-sensitive screen 1400 can be complemented by an interface deviceaccording to the invention. Reference numeral 1404 denotes an electrodewhich is an implementation of the electrodes described in connectionwith previously-described embodiments, such as the electrode 106described in connection with FIGS. 1 and 2. A supplemental insulator1402 may be positioned between the touch-sensitive screen 1400 and theinventive electrode 1404, in case the touch-sensitive screen 1400 itselffails to provide sufficient insulation.

In addition to conventional touch-screen functionality, namely detectionof approaching or touching by the touch-sensitive areas by the user'sfinger, the controller 1406 uses information of the position of thefinger 120 to temporally vary the intensity of the electrosensorystimulation invoked by the electrode 1404 on the finger 120. Althoughthe intensity of the electrosensory stimulation is varied over time,time is not an independent variable in the present embodiment. Instead,timing of the temporal variations is a function of the position of thefinger 120 relative to the touch-sensitive areas (here: A₁, A₂ and A₃).Thus it is more accurate to say that the present embodiment is operableto cause variations in the intensity of the electrosensory stimulationinvoked by the electrode 1404 on the finger 120, wherein the variationsare based on the position of the finger 120 relative to thetouch-sensitive areas.

The bottom side of FIG. 14 illustrates this functionality. The threetouch-sensitive area A₁, A₂ and A₃ are demarcated by respective xcoordinate pairs {x₁, x₂}, {x₃, x₄} and {x₅, x₇}. Processing in the ydirection is analogous and a detailed description is omitted. Thecontroller 1406 does not sense the presence of the finger, or senses thefinger as inactive, as long as the finger is to the left of any of thetouch-sensitive areas A₁, A₂ and A₃. In this example the controller 1406responds by applying a low-intensity signal to the electrode 1404. Assoon as the finger 120 crosses the x coordinate value x₁, the controller1406 detects the finger over the first touch-sensitive area A₁ andstarts to apply a medium-intensity signal to the electrode 1404. Betweenthe areas A₁ and A₂ (between x coordinates x₂ and x₃), the controlleragain applies a low-intensity signal to the electrode 1404. The secondtouch-sensitive area A₂ is processed similarly to the firsttouch-sensitive area A₁, but the third touch-sensitive area A₃ isprocessed somewhat differently. As soon as the controller 1406 detectsthe finger 120 above or in close proximity to the area A₃, it begins toapply the medium-intensity signal to the electrode 1404, similarly toareas A₁ and A₂. But the user decides to press the touch screen 1400 ata point x₆ within the third area A₃. The controller 1406 detects thefinger press (activation of the function assigned to the area A₃) andresponds by applying a high intensity signal to the electrode 1404.

Thus the embodiment shown in FIG. 14 can provide the user with a tactilefeedback which creates an illusion of a textures surface, although onlya single electrode 1404 was used to create the electrosensory stimulus.A residual problem is, however, that the user has to memorize thesignificance of the several touch-sensitive areas or obtain visual oraural information on their significance.

FIG. 15 shows a further enhanced embodiment from the one described inconnection with FIG. 14. The embodiment shown in FIG. 15 uses differenttemporal variations of the intensity of the electrosensory stimulus,wherein the different temporal variations provide the user with atactile feedback indicating the significance of the touch-sensitiveareas.

The operation of the embodiment shown in FIG. 14 differs from the onedescribed in connection with FIG. 14 in that the controller, heredenoted by reference numeral 1506, applies different temporal variationsto the intensity of the signal to the electrode 1404. In this example,the first touch-sensitive area A₁ is processed similarly to thepreceding embodiment, or in other words, the intensity of theelectrosensory stimulus depends only on the presence of the finger 120in close proximity to the area A₁. But in close proximity to areas A₂and A₃, the controller 1506 also applies temporal variations to theintensity of the electrosensory stimulus. For example the significance(coarsely analogous with a displayed legend) of area A₂ is indicated bya pulsed electrosensory stimulus at a first (low) repetition rate, whilethe significance of area A₃ is indicated by a pulsed electrosensorystimulus at a second (higher) repetition rate. In an illustrativeexample, the three touch-sensitive areas A₁, A₂ and A₃ can invoke thethree functions in a yes/no/cancel-type user interface, wherein the usercan sense the positions of the user interface keys (here: the threetouch-sensitive areas) and the indication of an accepted input only viatactile feedback. In other words, the user needs no visual or auralinformation on the positions of the touch-sensitive areas or on theselected function. The embodiment described in connection with FIG. 15is particularly attractive in car navigators or the like, which shouldnot require visual attention from their users.

In the embodiments shown in FIGS. 14 and 15, when the user's finger 120has selected the function assigned to area A₃ and the controller CTRL1406, 1506 generates the high-intensity electrosensory stimulus via theelectrode 1404, the high-intensity stimulus is sensed via any of theareas A₁, A₂ and A₃. In other words, if one finger of the user pressesthe area A₃, other finger(s) in close proximity to the other areas A₂and/or A₃ will also sense the high-intensity stimulus. In cases wherethis is not desirable, the embodiments shown in FIGS. 14 and 15 can becombined with the multi-electrode embodiment disclosed in connectionwith FIG. 9, such that the signal to each of several electrodes (shownin FIG. 9 as items 910 a through 910 i) is controlled individually.

It is readily apparent to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

REFERENCES

-   1. Gunther, Eric: “Skinscape: A Tool for Composition in the Tactile    Modality” Master's thesis, Massachusetts Institute of Technology    2001, available on the Internet address:    http://mf.media.mit.edu/pubs/thesis/guntherMS.pdf

What is claimed is:
 1. An apparatus comprising: a conductor configuredto have a variable electrical charge that generates an attractive forcebetween the conductor and a body member; an insulator configured toelectrically insulate the body member from the conductor; and acontroller configured to vary the attractive force generated between theconductor and the body member by controlling the variable electricalcharge of the conductor in accordance with an electrical signal at afirst frequency, the electrical signal having an envelope defined by atleast a second frequency that is less than the first frequency of theelectrical signal and that modulates the first frequency of theelectrical signal.
 2. The apparatus of claim 1, wherein: the controlleris configured to vary the attractive force generated between theconductor and the body member in a pattern of pulses with a repetitionrate in a range of 10 Hz to 1000 Hz.
 3. The apparatus of claim 2,wherein: the controller is configured to vary the attractive force inthe pattern of pulses with the repetition rate between 50 Hz and 500 Hz.4. The apparatus of claim 1, wherein: the controller is configured toset the first frequency of the electrical signal between 1 kHz and 1MHz.
 5. The apparatus of claim 1, wherein: the envelope of theelectrical signal is defined by at least the second frequency and athird frequency that modulates the second frequency.
 6. The apparatus ofclaim 1, wherein: the conductor is a first insulated electrodepositioned to stimulate a first portion of the body member; the variableelectrical charge that generates the attractive force is a firstvariable electrical charge that generates a first attractive forcebetween the first insulated electrode and the first portion of the bodymember; the apparatus further comprises a second insulated electrodepositioned to stimulate a second portion of the same body member; andwherein the controller is configured to control the first variableelectrical charge separately from controlling a second variableelectrical charge that generates a second attractive force between thesecond insulated electrode and the second portion of the same bodymember.
 7. The apparatus of claim 6, wherein: the controller isconfigured to individually vary the first and second attractive forcesin accordance with a spatially variant tactile pattern selected from thegroup consisting of a leftward sweep, a rightward sweep, an upwardsweep, a downward sweep, a clockwise rotation, and an anti-clockwiserotation.
 8. The apparatus of claim 1, wherein: the controller isconfigured to vary the attractive force generated between the conductorand the body member by varying the electrical signal whose envelope isdefined by at least the second frequency.
 9. The apparatus of claim 8,wherein: the controller is configured to control the variable electricalcharge of the conductor in accordance with a third frequency thatmodulates the second frequency of the electrical signal, the secondfrequency modulating the first frequency of the electrical signal. 10.The apparatus of claim 1, further comprising: a sensor configured todetect a location on the insulator at which the body member contactsinsulator; and wherein the controller is configured to control thevariable electrical charge of the conductor based on the detectedlocation at which the body member contacts the insulator.
 11. Theapparatus of claim 1, further comprising: a touch-sensitive screenconfigured to detect a change in pressure exerted by the body member ona portion of the touch-sensitive screen; and the controller isconfigured to control the variable electrical charge of the conductorbased on the change in pressure exerted by the body member and detectedby the touch-sensitive screen.
 12. An apparatus comprising: a conductorconfigured to have a variable electrical charge that generates anattractive force between a conductor and a body member; an insulatorconfigured to electrically insulate the body member from the conductor;a touch-sensitive screen configured to detect that the body membertouches the apparatus at a location that corresponds to a portion of thetouch-sensitive screen; and a controller configured to vary theattractive force generated between the body member and the conductor atthe location on the apparatus by controlling the variable electricalcharge of the conductor in accordance with an electrical signal at afirst frequency, the electrical signal having an envelope defined by atleast a second frequency that is less than the first frequency of theelectrical signal and that modulates the first frequency of theelectrical signal.
 13. The apparatus of claim 12, wherein: thecontroller is configured to vary the attractive force generated betweenthe conductor and the body member in a pattern of pulses with arepetition rate in a range of 10 Hz to 1000 Hz.
 14. The apparatus ofclaim 12, wherein: the envelope of the electrical signal is defined byat least the second frequency and a third frequency that modulates thesecond frequency.
 15. The apparatus of claim 12, wherein: the conductoris a first insulated electrode positioned to stimulate a first portionof the body member, the variable electrical charge that generates theattractive force is a first variable electrical charge that generates afirst attractive force between the first insulated electrode and thefirst portion of the body member; the apparatus further comprises asecond insulated electrode positioned to stimulate a second portion ofthe same body member; and wherein the controller is configured tocontrol the first variable electrical charge separately from controllinga second variable electrical charge that generates a second attractiveforce between the second insulated electrode and the second portion ofthe same body member.
 16. The apparatus of claim 15, wherein: thecontroller is configured to individually vary the first and secondattractive forces in accordance with a spatially variant tactile patternselected from the group consisting of a leftward sweep, a rightwardsweep, an upward sweep, a downward sweep, a clockwise rotation, and ananti-clockwise rotation.
 17. The apparatus of claim 12, wherein: thecontroller is configured to vary the attractive force generated betweenthe conductor in the body member by varying the electrical signal whoseenvelope is defined by at least the second frequency.
 18. The apparatusof claim 17, wherein: the controller is configured to control thevariable electrical charge of the conductor in accordance with a thirdfrequency that modulates the second frequency of the electrical signal,the second frequency modulating the first frequency of the electricalsignal.
 19. A method of controlling an attractive force between aconductor and a body member that is electrically insulated from theconductor, the method comprising: varying the attractive force betweenthe body member and the conductor by controlling a variable electricalcharge of the conductor in accordance with an electrical signal whoseenvelope is defined by at least a first frequency that is less than asecond frequency of the electrical signal and that modulates the secondfrequency of the electrical signal, the variable electrical charge ofthe conductor generating the attractive force between a conductor andthe body member.
 20. The method of claim 19, wherein: the varying of theattractive force by controlling the variable electrical charge includescontrolling the variable electrical charge of the conductor inaccordance with a third frequency that modulates the second frequency ofthe electrical signal, the second frequency modulating the firstfrequency of the electrical signal, and the envelope of the electricalsignal defines an intensity envelope of the attractive force generatedbetween the conductor and the body member.